Two-stage electrodialysis system and method for recovering waste co2-lean amine solvent

ABSTRACT

A two-stage electrodialysis system and a method for recovering waste CO2-lean amine solvent are provided. The system includes an amine solution pretreatment filtering system, a C-A homogeneous membrane electrodialysis device, a BP-A bipolar membrane electrodialysis system, and a CO2 recovery and capture system. The C-A homogeneous membrane electrodialysis system includes a material chamber, a C-A homogeneous membrane electrodialysis device, a concentrated HSSs waste solution chamber, an electrode solution chamber, and corresponding pipelines and peristaltic pumps. The BP-A bipolar membrane electrodialysis system includes a secondary feed chamber, a BP-A bipolar membrane electrodialysis device, an acid liquor chamber, an electrode solution chamber, and corresponding pipelines and peristaltic pumps. The waste CO2-lean amine solvent enters the material chamber after passing through the amine solution pretreatment filtering system. The concentrated HSSs waste solution chamber is connected to the secondary feed chamber by a buffer tank.

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims the benefit and priority of ChinesePatent Application No. 202111533765.8, entitled “Two-stageElectrodialysis System and Method for Recovering Waste CO₂-Lean AmineSolvent” filed on Dec. 15, 2021, the disclosure of which is incorporatedby reference herein in its entirety as part of the present application.

TECHNICAL FIELD

The present disclosure belongs to the technical field of recovery andtreatment of industrial organic waste solution, and in particularrelates to a two-stage electrodialysis system and a method forrecovering waste CO₂-lean amine solvent.

BACKGROUND ART

In a device for chemically absorbing CO₂, the reaction of absorbing CO₂by organic amine is expressed by following formula 1-1. By taking MEA(2-Aminoethanol) as an example, organic amine molecules and CO₂ aresubjected to a reversible reaction to produce carbamate and protonatedamine. However, due to the existence of a small number of impurities,such as O₂, SO₂ and NO₂, in the coal-fired flue gas, and the impuritiesin an absorbent, the organic amine absorbent may be subjected to anirreversible chemical reaction with these impurities. These irreversiblereactions are collectively known as degradation reaction. Differentdegradation processes, including thermal degradation and oxidativedegradation, often occur simultaneously to produce a set of degradationproducts. The literature at present reported that the degradationproducts were up to 100 or more species.

Amine degradation products are divided into neutral degradation productsand heat-stable salts (HSSs) based on whether the amine degradationproducts maintain electric neutrality in a solution. The neutralproducts include amides, organic acids, imidazole, piperazine, HEEDA,HEIA, urea and other organic substances; and HSSs are salts formed bythe reaction of amines as well as their acidic degradation products andimpurities (such as organic acids and hydrochloric acid). These saltsmainly include formic acid, acetic acid, ethanoic acid, oxalic acid,sulfate, and the like, which cannot be regenerated in the desorptiontower. The tests showed that the amine loss rate in the process forchemically absorbing CO₂ is about 1.6 to 3.1 kgMEA/tCO₂, in which theloss caused by degradation accounts for about 35%. The degradationproducts, especially the accumulation of HSS⁻ in the absorbent, causenot only the loss of the organic amine in the absorbent but also aseries of operation problems. In general, the accumulation of HSSs inthe absorbent may cause the following problems.

1. The CO₂ absorption capacity of the absorbent is reduced, which makesthe overall performance of the system deteriorate.

2. The viscosity is increased and the mass transfer efficiency isreduced, which increases the solvent cycle cost.

3. The equipment is corroded by HSSs.

4. The gas-solution specific surface area is reduced by solutionfoaming.

The maximum allowable concentration of HSSs in the CCS industrial systemis 0.5 wt % (5000 ppm), while the optimal concentration of HSSs for thestable operation of the device should be less than 500 ppm. Therefore,the removal of heat-stable salts and the recycling of organic amineabsorbent have a great significance for ensuring the long-term stableoperation of the whole CCS system.

Electrodialysis (ED) devices migrate anions from one solution chamber toanother solution chamber in a directional manner under the action ofanion and cation exchange membranes and an electric field. As adesalination technology, the ED has been widely used in the desalinationindustry since the 1950s. The application of the ED method to organicamine absorbents to remove HSSs was developed by the Dow chemicalcompany in the early 1990s. A commercial ED device may include hundredsof stacked membrane stacks. When a voltage is applied to two electrodes,positive ions and negative ions move towards opposite electrodes andpass through the ion exchange membranes. The final effect is thationized anions and cations are removed from a feed stream and arecollected in a concentration chamber. At present, the ED technology hasbeen successfully used for HSSs removal in refineries. However, thereare very few cases of recovery using the ED technology in processes forchemically absorbing CO₂. In addition, in the process of removing HSS⁻by the traditional ED device, a neutral amine degradation product mayremain in the solution, while some carbamate anions and protonatedamines are transferred and lost. The loss rate may reach about 15%-20%,thereby leading to the waste of the amine solution. The producedhigh-concentrated amine-containing waste solution still needs to bespecially treated, which increases the treatment cost.

SUMMARY

For the shortcomings in the prior art, a two-stage electrodialysissystem for recovering waste CO₂-lean amine solvent is provided toachieve removal of HSSs in the organic amine waste solution, thusperforming secondary recycling. An obtained purified amine solution hasa concentration of less than 500 ppm, defects of the traditionalelectrodialysis recovery device are overcome, an amine loss rate is low,and no additional waste solution is generated.

A two-stage electrodialysis system for recovering waste CO₂-lean aminesolvent, the system includes an amine solution pretreatment filteringsystem, a C-A homogeneous membrane electrodialysis system, a BP-Abipolar membrane electrodialysis system, and a CO₂ recovery and capturesystem.

The C-A homogeneous membrane electrodialysis system includes a materialchamber, a C-A homogeneous membrane electrodialysis device, aconcentrated HSSs waste solution chamber, and an electrode solutionchamber. A first loop is formed by connecting the material chamber andthe C-A homogeneous membrane electrodialysis device through firstpipelines and a first peristaltic pump. A second loop is formed byconnecting the concentrated HSSs waste solution chamber and the C-Ahomogeneous membrane electrodialysis device through second pipelines anda second peristaltic pump. A third loop is formed by connecting theelectrolyte solution chamber and the C-A homogeneous membraneelectrodialysis device through third pipelines and a third peristalticpump.

The BP-A bipolar membrane electrodialysis system includes a secondaryfeed chamber, a BP-A bipolar membrane electrodialysis device, an acidliquor chamber and an electrode solution chamber. A fourth loop isformed by connecting the secondary feed chamber and the BP-A bipolarmembrane electrodialysis device through fourth pipelines and a fourthperistaltic pump. A fifth loop is formed by connecting the acid liquorchamber and the BP-A bipolar membrane electrodialysis device throughfifth pipelines and a fifth peristaltic pump. A sixth loop is formed byconnecting the electrode solution chamber and the BP-A bipolar membraneelectrodialysis device through sixth pipelines and the third peristalticpump.

A to-be-treated waste CO₂-lean amine solvent enters the material chamberof the C-A homogeneous membrane electrodialysis system after passingthrough the amine solution pretreatment filtering system. Theconcentrated HSSs waste solution chamber is connected to the secondaryfeed chamber by a buffer tank. An upper part of the buffer tank isconnected to the CO₂ recovery and capture system by seventh pipelines.Acid liquor generated in the acid liquor chamber is introduced into thebuffer tank by eighth pipelines.

In some embodiments, a concentration of HSS⁻ in the waste CO₂-lean aminesolvent may be more than 1500 ppm and a conductivity of the wasteCO₂-lean amine solvent is more than 8.0 ms/cm. After passing through alean solution cooler, the waste CO₂-lean amine solvent is partiallycirculated in the system until the concentration of the HSS⁻ may be lessthan 500 ppm and the conductivity of the waste CO₂-lean amine solvent isless than 2.0 ms/cm, and flows back to a system for chemically absorbingCO₂ for circulation.

In some embodiments, CO₂ produced by desorption in the buffer tank maybe fed into a CO₂ purifying pipeline in a system for chemicallyabsorbing CO₂ for compression, liquidation and storage, after the CO₂may be pressurized by the CO₂ recovery and capture system.

A method for recovering waste CO₂-lean amine solvent the method beingcarried out by the two-stage electrodialysis system, the methodincludes:

removing solid impurities from the waste CO₂-lean amine solvent by theamine solution pretreatment filtering system to from another wasteCO₂-lean amine solvent, introducing the another waste CO₂-lean aminesolvent into the material chamber and the concentrated HSSs wastesolution chamber of the C-A homogeneous membrane electrodialysis system,and turning on a DC power supply of the C-A homogeneous membraneelectrodialysis system and the first peristaltic pump, the secondperistaltic pump and the third peristaltic pump; starting to circulatethe another waste CO₂-lean amine solvent in the material chamber, aconcentrated HSSs waste solution produced by the concentrated HSSs wastesolution chamber and an electrode solution, enabling HSS⁻ rich in theanother waste CO₂-lean amine solvent in the material chamber to transferinto the concentrated HSSs waste solution chamber through anion exchangemembranes of the C-A homogeneous membrane electrodialysis system,enabling a concentration of HSS⁻ in the material chamber to decreasecontinuously; and feeding the another waste CO₂-lean amine solvent inthe material chamber with the concentration of HSS⁻ less than 500 ppmback to the system for chemically absorbing CO₂ for circulation, afterthe concentration of HSS⁻ in the material chamber is less than 500 ppm;and

feeding produced concentrated HSSs waste solution into the buffer tank,and into the secondary feed chamber and the acid liquor chamber of theBP-A bipolar membrane electrodialysis system after adding acid liquor,and turning on a DC power supply of the BP-A bipolar membraneelectrodialysis system and the third peristaltic pump, the fourthperistaltic pump and the fifth peristaltic pump for circulation;enabling OH⁻ and H⁺ produced by a bipolar membrane to enter thesecondary feed chamber and the acid liquor chamber, respectively, andenabling HSS⁻ in the secondary feed chamber to enter the acid liquorchamber through the anion exchange membrane, enabling a concentration ofthe HSS⁻ in the secondary feed chamber to decrease continuously, andfeeding the concentrated HSSs waste solution in the secondary feedchamber into the material chamber of the C-A homogeneous membraneelectrodialysis system through the first pipelines, and subsequentlyback to the system for chemically absorbing CO₂ for circulation, afterthe concentration of the HSS⁻ in the second feed chamber is less than500 ppm; wherein acid produced in the acid liquor chamber is configuredfor desorption of CO₂ in the buffer tank and for cleaning a subsequentmembrane stack of the C-A homogeneous membrane electrodialysis systemand a subsequent membrane stack of the BP-A bipolar membraneelectrodialysis system.

In some embodiments, the membrane stack of the C-A homogeneous membraneelectrodialysis system may include more than five anion exchangemembranes and more than five first cation exchange membranes. Each ofthe more than five anion exchange membranes and a corresponding one ofthe more than five first cation exchange membranes may be paired. Themore than five anion exchange membranes and the more than five firstcation exchange membranes membrane may be arranged alternately insequence of one cation exchange membrane C, one anion exchange membraneA, and another one cation exchange membrane C. The membrane stack of theBP-A bipolar membrane electrodialysis system may include more than fivebipolar membranes and more than five second anion exchange membranes.Each of the more than five bipolar membranes and a corresponding one ofthe more than five second anion exchange membranes may be paired. Themore than five bipolar membranes and the more than five anion exchangemembranes may be alternately arranged in sequence of one bipolarmembrane BP, one anion membrane A, and another one bipolar membrane BP.In some embodiments, the electrode solution in the electrode solutionchamber in each of the C-A homogeneous membrane electrodialysis systemand the BP-A bipolar membrane electrodialysis system may be a Na₂SO₄solution with a concentration of 0.1 to 1.0 mol/L.

In some embodiments, the DC power supply of the C-A homogeneous membraneelectrodialysis system may have a voltage of 0 to 15 V and an uppercurrent density limit of 400 A/m².

In some embodiments, the DC power supply of the BP-A bipolar membraneelectrodialysis system may have a voltage of 0 to 35 V and an uppercurrent density limit of 800 A/m².

In some embodiments, operation temperatures in the amine solutionpretreatment filtering system, the C-A homogeneous membraneelectrodialysis system and the BP-A bipolar membrane electrodialysissystem may be less than 40° C.

In accordance with the embodiments, a pretreatment mechanical filteringdevice is used for preliminarily treating waste CO₂-lean amine solvent,an obtained material with low solid impurity content and high HSS⁻ ionconcentration is fed into a C-A homogeneous membrane electrodialysisdevice, and is subjected to the removal of HSS⁻ to obtain a purifiedamine solution with a HSSs concentration below 500 ppm and aconcentrated waste solution with a high HSS concentration. Theconcentrated waste solution first enters the buffer tank, and enters thesecondary feed chamber and an acid liquor chamber of the BP-A bipolarmembrane electrodialysis device after adding excess acid liquor for CO₂desorption, thus further obtaining a purified amine solution and theacid liquor. The waste CO₂-lean amine solvent is continuously introducedinto the two-stage electrodialysis system to continuously obtain thatthe purified amine solution enters into the system for chemicallyabsorbing CO₂ for circulation. The system and the method provided by theembodiments not only can reduce a content of the HSSs in the wasteCO₂-lean amine solvent to obtain the purified amine solution and improvethe operation stability of the system for chemically absorbing CO₂, butalso can achieve secondary recycling of the concentrated HSSs wastesolution by the bipolar membrane system to further reduce the organicamine loss rate. In accordance with the whole system, no additionalwaste solution is produced, and the cost for handling the waste solutionis reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structure diagram of a two-stage electrodialysis system forrecovering waste CO₂-lean amine solvent according to the presentdisclosure.

List of the reference characters: 1 pretreatment mechanical filteringdevice; 2 material chamber; 3 C-A homogeneous membrane electrodialysisdevice; 4 concentrated HSSs waste solution chamber; 5 buffer tank; 6secondary feed chamber 6; 7 BP-A bipolar membrane electrodialysisdevice; 8 acid liquor chamber; 9 electrode solution chamber; 11 firstperistaltic pump; 12 second peristaltic pump; 13 third peristaltic pump;14 fourth peristaltic pump; 15 fifth peristaltic pump; 16 sixthperistaltic pump; and 17 seventh peristaltic pump.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure is further described in detail below withreference to the accompanying drawings and embodiments. It needs to benoted that the following embodiments are intended to facilitate theunderstanding of the present disclosure and do not set any limitthereon.

As shown in FIG. 1 , a two-stage electrodialysis system for recoveringwaste CO₂-lean amine solvent includes an amine solution pre-treatmentfiltering system, a C-A homogeneous membrane electrodialysis system, aBP-A bipolar membrane electrodialysis system and a CO₂ recovery andcapture system.

The C-A homogeneous membrane electrodialysis system includes a materialchamber 2, a C-A homogeneous membrane electrodialysis device 3, aconcentrated HSSs waste solution chamber 4, an electrode solutionchamber 9, and corresponding valves and pipelines. A loop is formed byconnecting the material chamber 2 and the C-A homogeneous membraneelectrodialysis device 3 through pipelines and a first peristaltic pump11. A loop is formed by connecting the concentrated HSSs waste solutionchamber 4 and the C-A homogeneous membrane electrodialysis device 3through pipelines and a second peristaltic pump 12. A loop is formed byconnecting the electrolyte solution chamber 9 and the C-A homogeneousmembrane electrodialysis device 3 through pipelines and a thirdperistaltic pump 13.

The BP-A bipolar membrane electrodialysis system includes a secondaryfeed chamber 6, a BP-A bipolar membrane electrodialysis device 7, anacid liquor chamber 8, an electrode solution chamber 9, andcorresponding valves and pipelines. A loop is formed by connecting thesecondary feed chamber 6 and BP-A bipolar membrane electrodialysisdevice 7 through pipelines and a fourth peristaltic pump 14. A loop isformed by connecting the acid liquor chamber 8 and the BP-A bipolarmembrane electrodialysis device 7 through pipelines and a fifthperistaltic pump 15. A loop is formed by connecting the electrodesolution chamber 9 and the BP-A bipolar membrane electrodialysis device7 through pipelines and the third peristaltic pump 13.

The concentrated HSSs waste solution chamber 4 is connected to thesecondary feed chamber 6 by a buffer tank 5. An upper part of the buffertank 5 is connected to the CO₂ recovery and capture system by pipelines.Acid liquor generated in the acid liquor chamber 8 is introduced intothe buffer tank 5 by pipelines.

The amine solution pretreatment filtering system includes a pretreatmentmechanical filtering device 1, inlet and outlet pipelines, a sixthperistaltic pump 16 at an outlet and valves, and can filter solidimpurities from the introduced waste solution. A to-be-treated wasteCO₂-lean amine solvent enters the material chamber 2 of the C-Ahomogeneous membrane electrodialysis system after passing through theamine solution pretreatment filtering system. The CO₂ recovery andcapture system includes a gas outlet pipeline above the buffer tank 5, aseventh peristaltic pump 17, and a subsequently connected CO₂ purifyinggas pipeline.

A method for recovering an waste CO₂-lean amine solvent using the systemabove includes the following steps.

The waste CO₂-lean amine solvent, after removing solid impurities by theamine solution pretreatment filtering system to from another wasteCO₂-lean amine solvent, is introduced into the material chamber 2 andthe concentrated HSSs waste solution chamber 4 of the C-A homogeneousmembrane electrodialysis system, and a DC power supply of the C-Ahomogeneous membrane electrodialysis system and the first peristalticpump 11, the second peristaltic pump 12 and the third peristaltic pump13 are turned on; the another waste CO₂-lean amine solvent in thematerial chamber 2, a concentrated HSSs waste solution produced by theconcentrated HSSs waste solution chamber 4 and an electrode solutionstart to circulate, heat-stable salt ions (HSS) rich in the anotherwaste CO₂-lean amine solvent in the material chamber 2 transfers intothe concentrated HSSs waste solution chamber 4 through anion exchangemembranes of the C-A homogeneous membrane electrodialysis system, aconcentration of the HSS⁻ in the material chamber 2 decreasescontinuously, and after the concentration of the HSS⁻ in the materialchamber 2 is less than 500 ppm, the another waste CO₂-lean amine solventin the material chamber 2 with the concentration of HSS⁻ less than 500ppm is fed back to the system for chemically absorbing CO₂ forcirculation.

Produced concentrated HSSs waste solution is fed into the buffer tank 5,and is fed into secondary feed chamber 6 and acid liquor chamber 8 ofthe BP-A bipolar membrane electrodialysis system after adding excessacid liquor, and a DC power supply of the BP-A bipolar membraneelectrodialysis system and the third peristaltic pump 13, the fourthperistaltic pump 14 and the fifth peristaltic pump 15 are turned on forcirculation. OH⁻ and H⁺ produced by a bipolar membrane enter thesecondary feed chamber 6 and the acid liquor chamber 8, respectively,and the HSS⁻ in the secondary feed chamber 6 enters the acid liquorchamber 8 through the anion exchange membranes, a concentration of theHSS⁻ in the secondary feed chamber 6 decreases continuously, and afterthe HSS⁻ concentration in the second feed chamber 6 is less than 500ppm, the concentrated HSSs waste solution in the secondary feed chamber6 is fed into the material chamber 2 of the C-A homogeneous membraneelectrodialysis system through pipelines, and is subsequently fed backto the system for chemically absorbing CO₂ for circulation. Acidproduced in the acid liquor chamber 8 is configured for desorption ofCO₂ in the buffer tank 5 and for cleaning a subsequent membrane stack ofthe C-A homogeneous membrane electrodialysis system and a subsequentmembrane stack of the BP-A bipolar membrane electrodialysis system.

The C-A homogeneous membrane electrodialysis system has the advantagesof high HSSs removal rate, low energy consumption and simple structure.The BP-A bipolar membrane electrodialysis system can produce OH⁻ and H⁺under the action of an electric field. OH⁻ is used to replace HSS⁻ inconcentrated HSSs waste solution, and H⁺ and HSS⁻ are combined togenerate a variety of acids in the acid liquor chamber, thus obtainingthe product which is a purified amine solution.

In accordance with the present disclosure, a concentration of an HSS⁻ inthe waste CO₂-lean amine solvent is more than 1500 ppm and aconductivity of the waste CO₂-lean amine solvent is more than 8.0 ms/cm.After passing through a lean solution cooler, the waste CO₂-lean aminesolvent is partially circulated in the system until the concentration ofthe HSS⁻ is less than 500 ppm and the conductivity is less than 2.0ms/cm, and flows back to a system for chemically absorbing CO₂ forcirculation. A membrane stack of the C-A homogeneous membraneelectrodialysis system includes ten anion exchange membranes and tencation exchange membranes, and each of the ten anion exchange membranesand a corresponding one of the ten cation exchange membranes are paired.A membrane stack of the BP-A bipolar membrane electrodialysis systemincludes ten bipolar membranes and ten anion exchange membranes, andeach of the ten bipolar membranes and a corresponding one of the tenanion exchange membrane are paired. A single membrane (any one of themembranes mentioned above) has an effective area of 55 cm². A singleanion exchange membrane has a thickness of 180 μm and a resistance of2.3 Ω/cm². A single cation exchange membrane has a thickness of 150 μmand a resistance is 1.9 omega/cm². A single bipolar membrane has athickness of 280-340 μm.

In this embodiment, an electrode solution for each of the C-Ahomogeneous membrane electrodialysis system and the BP-A bipolarmembrane electrodialysis system is a Na₂SO₄ solution with aconcentration of 0.5 mol/L. The DC power supply of the C-A homogeneousmembrane electrodialysis system has a voltage of 15 V and an uppercurrent limit of 2.2 A. The DC power supply of the BP-A bipolar membraneelectrodialysis system has a voltage of 35 V and an upper current limitof 4.4 A. An operation temperature of each of the amine solutionpretreatment filtering system, the C-A homogeneous membraneelectrodialysis system and the BP-A bipolar membrane electrodialysissystem is less than 40° C. A flow rate of each of the peristaltic pumpsfor the C-A homogeneous membrane electrodialysis system and the BP-Abipolar membrane electrodialysis system is 500 ml/min.

To verify the effect of the embodiment, the system of the presentdisclosure is carried out the recovery testing of the waste CO₂-leanamine solvent.

In the amine solution pretreatment filtering system, a flow rate of thesixth peristaltic pump 16 is 500 ml/min.

In the C-A homogeneous membrane electrodialysis system, ion membranesused in the C-A homogeneous membrane electrodialysis device 3 includeone anion membrane with model AGU and two cation membrane with modelCSE-2 produced by ASTOM Corporation. The ion exchange membranes arestacked alternately in sequence of one cation exchange membrane C, oneanion exchange membrane A, and another one cation exchange membrane C(i.e., C-A-C order), so as to form a single one group of membrane pairs.Ten membrane pairs are repeatedly stacked and fixed with an outer frameto form a membrane stack. The membrane stack is fixed to a middle of acathode plate and an anode plate, and the anode plate and the cathodeplate are connected to a positive electrode and a negative electrode ofthe DC power supply DC respectively to form the C-A homogeneous membraneelectrodialysis device 3. A single membrane (any one of the membranesmentioned above) has an effective area of 55 cm². A single cationexchange membrane has a thickness of 180 μm and a resistance of 2.3Ω/cm². A single anion exchange membrane has a thickness of 150 μm and aresistance of 1.9 Ω/cm². The membrane stack is separated by the ionmembranes to form the material chamber 2, the concentrated HSSs wastesolution chamber 4, and an electrode solution chamber 9 in sequence.Flow rates of the solution entering the C-A homogeneous membraneelectrodialysis device 3 from the material chamber 2, the concentratedHSSs waste solution chamber 4 and the electrode solution chamber 9 arerespectively controlled by the first peristaltic pump 11, the secondperistaltic 12 and the third peristaltic pump 13 to be 500 ml/min, thusforming three circulating loops which are a material loop, aconcentrated HSSs waste solution loop, and an electrode solution loop.

In the BP-A bipolar membrane electrodialysis system, an ion membraneused in the BP-A bipolar membrane electrodialysis device 7 include oneanion membrane with model AGU and two bipolar membranes with model BPUproduced by ASTOM Corporation. The ion exchange membranes are stacked insequence of one bipolar membrane BP, one anion membrane A, and anotherone bipolar membrane BP (i.e., BP-A-BP order), so as to form a singleone group of membrane pairs. Ten membrane pairs are repeatedly stackedand fixed with an outer frame to form the membrane stack. The membranestack is fixed to the middle of a cathode plate and an anode plate, andthe anode plate and the cathode plate are connected to the positiveelectrode and the negative electrode of the DC power supply DCrespectively to form the BP-A bipolar membrane electrodialysis device 7.A single membrane (any one of the membranes mentioned above) has aneffective area of 55 cm². A single cation exchange membrane has athickness of 180 μm and a resistance of 2.3 Ω/cm².

A single bipolar membrane has a thickness of 280-340 μm. The membranestack is separated by the ion membranes to form the secondary feedchamber 6, the acid liquor chamber 8, and an electrode solution chamber9 in sequence. Flow rates of the solution entering the BP-A bipolarmembrane electrodialysis device 7 from the secondary feed chamber 6, theacid liquor chamber 8, and the electrode solution chamber 9 arerespectively controlled by the fourth peristaltic pump 14, the fifthperistaltic 15 and the third peristaltic pump 13 to be 500 ml/min, thusforming three circulating loops which are a secondary feed loop, an acidliquor loop, and an electrode solution loop.

The waste CO₂-lean amine solvent is treated using the system above. Thewaste solution has an organic amine concentration of 23.8 wt %, aninitial HSSs concentration of 2000 ppm, a conductivity of 9.8 ms/cm, andCO₂ load of 0.15 mol/mol. After filtering the solid impurities from thewaste solution by the amine solution pretreatment filtering system, 1 Lof waste solution is added into the material chamber 2 and theconcentrated HSSs waste solution chamber 4 successively, and 1 L of 0.5mol/L sodium sulfate solution is added into the electrode solutionchamber 9. Three peristaltic pumps of the C-A homogeneous membraneelectrodialysis are turned on, and the DC power supply DC is turned onafter the flow rate is regulated to 500 ml/min, an output voltage is setto be 15 V and the upper current limit is set to be 2.2 A for operationof the system. After operating for 80 min, a conductivity of an aminesolution in the material chamber 2 is reduced to 0.6 ms/cm, aconductivity of the solution in the concentrated HSSs waste solutionchamber 4 is increased to 19.2 ms/cm, and the HSSs concentration in thematerial chamber 2 is reduced below 100 ppm. The DC power supply and thethree peristaltic pumps are turned off. The amine solution in thematerial chamber 2 is returned to the system for chemically absorbingCO₂ for circulating, and the concentrated HSSs waste solution is pumpedinto the buffer tank 5 for further treatment.

Excess acid liquor (the prepared dilute sulfuric acid is employed duringfirst being added, and the subsequent acid liquor is provided by theacid liquor chamber 8) is added into the amine solution in the buffertank 5, and the desorbed CO₂ enters a gas pipeline to be further pumpedinto the CO₂ purifying gas pipeline. The amine solution is respectivelypumped into the secondary feed chamber 6 and the acid liquor chamber 8by about 500 ml, and the concentration of the HSSs in both chambers isabout 4000 ppm. The three peristaltic pumps of the BP-A bipolar membraneelectrodialysis system are turned on. The DC power supply DC is turnedon after the flow rate is regulated to 500 ml/min. Further, the outputvoltage is set to be 25 V and the upper current limit is set to be 4.4 Afor operation. After operating for 30 min, the conductivity of the aminesolution in the secondary feed chamber 6 is decreased to 5.4 ms/cm, theconductivity in the acid liquor chamber is increased to 25.1 ms/cm, andthe HSSs concentration in the secondary feed chamber 6 is reduced below200 ppm. The DC power supply and the three peristaltic pumps are turnedoff. The solution in the secondary feed chamber 6 is returned to thematerial chamber 2, and the solution in the acid liquor chamber 8 isused for subsequent CO₂ desorption in the buffer tank 5 and for cleaningmembrane stack.

In accordance with the system, the waste organic amine solution in thesystem for chemically absorbing CO₂ is recovered and purified by usingthe two-stage electrodialysis device, and the purified organic amineabsorbent is obtained. The whole system does not produce waste solution,and has the characteristics of simple equipment, good HSSs removaleffect and small loss of organic amine.

The above embodiments are a detailed description of the technicalsolutions and beneficial effects of the present disclosure. It should beunderstood that the above are only specific embodiments of the presentdisclosure and are not intended to limit the present disclosure, and anymodifications, additions and equivalent replacements made within thescope of the principles of the present disclosure shall be included inthe scope of protection of the present disclosure.

What is claimed is:
 1. A two-stage electrodialysis system for recoveringwaste CO₂-lean amine solvent, the system comprising an amine solutionpretreatment filtering system, a C-A homogeneous membraneelectrodialysis system, a BP-A bipolar membrane electrodialysis system,and a CO₂ recovery and capture system; wherein the C-A homogeneousmembrane electrodialysis system comprises a material chamber, a C-Ahomogeneous membrane electrodialysis device, a concentrated HSSs wastesolution chamber, and an electrode solution chamber; a first loop isformed by connecting the material chamber and the C-A homogeneousmembrane electrodialysis device through first pipelines and a firstperistaltic pump; a second loop is formed by connecting the concentratedHSSs waste solution chamber and the C-A homogeneous membraneelectrodialysis device through second pipelines and a second peristalticpump; and a third loop is formed by connecting the electrolyte solutionchamber and the C-A homogeneous membrane electrodialysis device throughthird pipelines and a third peristaltic pump; the BP-A bipolar membraneelectrodialysis system comprises a secondary feed chamber, a BP-Abipolar membrane electrodialysis device, an acid liquor chamber and anelectrode solution chamber; a fourth loop is formed by connecting thesecondary feed chamber and the BP-A bipolar membrane electrodialysisdevice through fourth pipelines and a fourth peristaltic pump; a fifthloop is formed by connecting the acid liquor chamber and the BP-Abipolar membrane electrodialysis device through fifth pipelines and afifth peristaltic pump; and a sixth loop is formed by connecting theelectrode solution chamber and the BP-A bipolar membrane electrodialysisdevice through sixth pipelines and the third peristaltic pump; ato-be-treated waste CO₂-lean amine solvent enters the material chamberof the C-A homogeneous membrane electrodialysis system after passingthrough the amine solution pretreatment filtering system; theconcentrated HSSs waste solution chamber is connected to the secondaryfeed chamber by a buffer tank; an upper part of the buffer tank isconnected to the CO₂ recovery and capture system by seventh pipelines,and acid liquor generated in the acid liquor chamber is introduced intothe buffer tank by eighth pipelines.
 2. The two-stage electrodialysissystem for recovering waste CO₂-lean amine solvent according to claim 1,wherein CO₂ produced by desorption in the buffer tank is fed into a CO₂purifying pipeline in a system for chemically absorbing CO₂ forcompression, liquidation and storage, after the CO₂ is pressurized bythe CO₂ recovery and capture system.
 3. A method for recovering wasteCO₂-lean amine solvent the method being carried out by the two-stageelectrodialysis system, the system comprising an amine solutionpretreatment filtering system, a C-A homogeneous membraneelectrodialysis system, a BP-A bipolar membrane electrodialysis system,and a CO₂ recovery and capture system; wherein the C-A homogeneousmembrane electrodialysis system comprises a material chamber, a C-Ahomogeneous membrane electrodialysis device, a concentrated HSSs wastesolution chamber, and an electrode solution chamber; a first loop isformed by connecting the material chamber and the C-A homogeneousmembrane electrodialysis device through first pipelines and a firstperistaltic pump; a second loop is formed by connecting the concentratedHSSs waste solution chamber and the C-A homogeneous membraneelectrodialysis device through second pipelines and a second peristalticpump; and a third loop is formed by connecting the electrolyte solutionchamber and the C-A homogeneous membrane electrodialysis device throughthird pipelines and a third peristaltic pump; the BP-A bipolar membraneelectrodialysis system comprises a secondary feed chamber, a BP-Abipolar membrane electrodialysis device, an acid liquor chamber and anelectrode solution chamber; a fourth loop is formed by connecting thesecondary feed chamber and the BP-A bipolar membrane electrodialysisdevice through fourth pipelines and a fourth peristaltic pump; a fifthloop is formed by connecting the acid liquor chamber and the BP-Abipolar membrane electrodialysis device through fifth pipelines and afifth peristaltic pump; and a sixth loop is formed by connecting theelectrode solution chamber and the BP-A bipolar membrane electrodialysisdevice through sixth pipelines and the third peristaltic pump; ato-be-treated waste CO₂-lean amine solvent enters the material chamberof the C-A homogeneous membrane electrodialysis system after passingthrough the amine solution pretreatment filtering system; theconcentrated HSSs waste solution chamber is connected to the secondaryfeed chamber by a buffer tank; an upper part of the buffer tank isconnected to the CO₂ recovery and capture system by seventh pipelines,and acid liquor generated in the acid liquor chamber is introduced intothe buffer tank by eighth pipelines; the method comprising: removingsolid impurities from the waste CO₂-lean amine solvent by the aminesolution pretreatment filtering system to from another waste CO₂-leanamine solvent, introducing the another waste CO₂-lean amine solvent intothe material chamber and the concentrated HSSs waste solution chamber ofthe C-A homogeneous membrane electrodialysis system, and turning on a DCpower supply of the C-A homogeneous membrane electrodialysis system andthe first peristaltic pump, the second peristaltic pump and the thirdperistaltic pump; starting to circulate the another waste CO₂-lean aminesolvent in the material chamber, a concentrated HSSs waste solutionproduced by the concentrated HSSs waste solution chamber and anelectrode solution, enabling HSS⁻ rich in the another waste CO₂-leanamine solvent in the material chamber to transfer into the concentratedHSSs waste solution chamber through anion exchange membranes of the C-Ahomogeneous membrane electrodialysis system, enabling a concentration ofHSS⁻ in the material chamber to decrease continuously; and feeding theanother waste CO₂-lean amine solvent in the material chamber with theconcentration of HSS⁻ less than 500 ppm back to the system forchemically absorbing CO₂ for circulation, after the concentration ofHSS⁻ in the material chamber is less than 500 ppm; and feeding producedconcentrated HSSs waste solution into the buffer tank, and into thesecondary feed chamber and the acid liquor chamber of the BP-A bipolarmembrane electrodialysis system after adding acid liquor, and turning ona DC power supply of the BP-A bipolar membrane electrodialysis systemand the third peristaltic pump, the fourth peristaltic pump and thefifth peristaltic pump for circulation; enabling OH⁻ and H⁺ produced bya bipolar membrane to enter the secondary feed chamber and the acidliquor chamber, respectively, and enabling HSS⁻ in the secondary feedchamber to enter the acid liquor chamber through the anion exchangemembranes, enabling a concentration of the HSS⁻ in the secondary feedchamber to decrease continuously, and feeding the concentrated HSSswaste solution in the secondary feed chamber into the material chamberof the C-A homogeneous membrane electrodialysis system through the firstpipelines, and subsequently back to the system for chemically absorbingCO₂ for circulation, after the concentration of the HSS⁻ in the secondfeed chamber is less than 500 ppm; wherein acid produced in the acidliquor chamber is configured for desorption of CO₂ in the buffer tankand for cleaning a subsequent membrane stack of the C-A homogeneousmembrane electrodialysis system and a subsequent membrane stack of theBP-A bipolar membrane electrodialysis system.
 4. The method forrecovering the waste CO₂-lean amine solvent according to claim 3,wherein the membrane stack of the C-A homogeneous membraneelectrodialysis system comprises more than five anion exchange membranesand more than five first cation exchange membranes, each of the morethan five anion exchange membranes and a corresponding one of the morethan five first cation exchange membranes are paired; the more than fiveanion exchange membranes and the more than five first cation exchangemembranes membrane are arranged alternately in sequence of one cationexchange membrane C, one anion exchange membrane A, and another onecation exchange membrane C; the membrane stack of the BP-A bipolarmembrane electrodialysis system comprises more than five bipolarmembranes and more than five second anion exchange membranes, each ofthe more than five bipolar membranes and a corresponding one of the morethan five second anion exchange membranes are paired, and the more thanfive bipolar membranes and the more than five anion exchange membranesare alternately arranged in sequence of one bipolar membrane BP, oneanion membrane A, and another one bipolar membrane BP.
 5. The method forrecovering the waste CO₂-lean amine solvent according to claim 3,wherein the electrode solution in the electrode solution chamber in eachof the C-A homogeneous membrane electrodialysis system and the BP-Abipolar membrane electrodialysis system is a Na₂SO₄ solution with aconcentration of 0.1 to 1.0 mol/L.
 6. The method for recovering thewaste CO₂-lean amine solvent according to claim 3, wherein the DC powersupply of the C-A homogeneous membrane electrodialysis system has avoltage of 0 to 15 V and an upper current density limit of 400 A/m². 7.The method for recovering the waste CO₂-lean amine solvent according toclaim 3, wherein the DC power supply of the BP-A bipolar membraneelectrodialysis system has a voltage of 0 to 35 V and an upper currentdensity limit of 800 A/m².
 8. The method for recovering the wasteCO₂-lean amine solvent according to claim 3, wherein operationtemperatures in the amine solution pretreatment filtering system, theC-A homogeneous membrane electrodialysis system and the BP-A bipolarmembrane electrodialysis system are less than 40° C.
 9. The method forrecovering the waste CO₂-lean amine solvent according to claim 3,wherein CO₂ produced by desorption in the buffer tank is fed into a CO₂purifying pipeline in a system for chemically absorbing CO₂ forcompression, liquidation and storage, after the CO₂ is pressurized bythe CO₂ recovery and capture system.